A magnetic resonance imaging apparatus (the MRI apparatus) is an apparatus for observing an echo signal (the MR echo signal) emitted from a subject after an RF pulse is emitted to the subject, to obtain a sectional image of the subject. In general, the MRI apparatus requires a plurality of echo signals to obtain one image. When frequencies and phases of the echo signals are analyzed, the sectional image can be obtained. Therefore, in acquiring these echo signals, respective frequencies of the emitted RF pulses need to be constant. For the emission of the RF pulses, a transmission coil is used, and for the reception of the echo signals, a reception coil is used.
A digital signal obtained by digitalizing the echo signal received through the reception coil in an analog-digital converter (ADC) is wirelessly transmitted, whereby the reception coil is made to be wireless. This system is known by U.S. Pat. No. 5,384,536 (hereinafter referred to as Reference 1).
When the echo signal is digitalized in this manner, a frequency of a clock signal which is used to drive the ADC (hereinafter referred to as the second clock signal) needs to match a frequency of a clock signal which is used to generate the RF pulse (hereinafter referred to as the first clock signal). When these frequencies of the first and second clock signals are different from each other, the phase of the digitalized echo signal change according to time, and accuracy of the sectional image reconstructed from this echo signal deteriorates.
In Reference 1, the first clock signal is wirelessly transmitted as a reference signal, and on the basis of this reference signal, the second clock signal is generated.
In a case where the system of Reference 1 is used and the reference signal is transmitted without any deterioration, the second clock signal can accurately be synchronized with the first clock signal. However, usually in the wireless transmission, noises are added to a transmission signal passed through various apparatuses for the wireless transmission. Moreover, during the wireless transmission, the transmission signal is distorted owing to multipath phasing or Doppler shift. In consequence, it is difficult to wirelessly transmit the reference signal without any deterioration, and the frequency of the second clock signal generated on the basis of the deteriorated reference signal might be different from that of the first clock signal.
From such a situation, it has been desired to suppress accuracy deterioration of the sectional image due to influence of the phase shift which occurs in the magnetic resonance echo signal during the digitalization of the magnetic resonance echo signal.